For example, a digital protection control measurement device for an electric power system converts a current or a voltage from an electric power system into digital data via a transformer (PCT: potential current transformer), an analog filter, and an analog-to-digital converter, performs an arithmetic operation on the digital data by software, and controls a breaker, an alarm device, or the like based on the arithmetic operation result.
In such a protection control measurement device that performs protection control on the electric power system, its measurement accuracy mainly depends on the input transformer (PCT), the analog filter, and the analog-to-digital converter (hereinafter, collectively referred to as “analog input unit”). In order to improve the performance of the protection control measurement device, the analog input unit has to have higher accuracy. In addition, the analog filter and the like are aged-deteriorated, and hence monitoring the aged deterioration at high accuracy is also necessary.
As a conventional technique of performing protection control on the electric power system, for example, a digital protection relay that performs over-sampling on digital data obtained by converting an analog signal in the analog input unit, and uses the data to reduce noise of the analog input unit has been proposed.
Further, as a monitoring method for the analog input unit, for example, a technique of monitoring superposed harmonics has been proposed.
In this monitoring method, in order to constantly monitor aged deterioration of components of the analog filter, a signal having a frequency equal to a frequency of a commercial electric power (50 Hz or 60 Hz) flowing through the electric power system is superimposed on an input to the analog filter and the magnitude, the phase, and the like thereof are monitored using software.
However, with the technique of a related art, the over-sampling accuracy depends on the performance of the analog-to-digital converter, and hence using a general-purpose converter causes a problem that the over-sampling accuracy may be too low to reduce the noise of the analog input unit.
Further, with the technique of a related art, the monitoring result has low reliability because the monitoring result largely depends on harmonics generating on the electric power system side.
Embodiments have been made in order to solve the above-mentioned problems and it is an object that to provide a protection relay device and a protection relay method that are capable of reducing noise generating in an analog input unit that receives a signal from an electric power system and also capable of monitoring aged deterioration of components of the analog input unit at high accuracy and reliability.